In the past, as is well known, the propulsive mechanism of nearly all watercraft was located at the stern (rear) of the craft (the sole exceptions being side-wheelers, long obsolete, or air/jet propelled craft such as hovercraft where the jet or propeller is above the craft). In outboard systems, the outboard motor is nearly always hung from the transom of the boat (some specialized work boats have an indentation into the transom, so that the outboard is slightly forward of the transom in a well). Even if the motor is located inboard toward the center or front (bow) of the boat, the propeller or jet exhaust is at the stern, either protruding from the transom (inboard/outboard or "Z" drive) or underneath.
In most inboard-motor cases, the steering of the watercraft is done by means of a steerable vane (the rudder) extending beneath the craft into the water. Jet-boats steer the jet exhaust at the rear of the craft, and outboards and inboard/outboards steer the drive unit or the entire motor/drive unit, usually through a limited range of 45.degree. or so either side of center (although some earlier outboards and some very small trolling motors can be swiveled 360.degree., eliminating the need for a reversing gear).
In some very large ocean-going craft or tugboats, separate fixed propellers (called side-thrusters) may be mounted internally near the bow, set to propel water out either side of the ship. These side-thrusters are used for maneuvering the ship sideways into dock or (in the case of tugs) for maneuvering the tug relative to a ship. They are not steerable, and cannot provide propulsion under normal circumstances. That function is still performed by one or more propellers under the stern.
Placing the drive mechanism of a watercraft in the back has the same disadvantages which have recently led to the near-total replacement of rear-wheel drive automobiles with front-wheel drive--only worse, since watercraft have the steering in the rear as well. The result is inherent instability. Upon application of power, the boat tends to rear up and turn. Propelling and steering the boat from the rear is analogous to balancing a broom on the hand, instead of gripping it at the top of the handle.